The invention relates to a fuel injection device operating on the solid-state energy storage principle, more particularly for two-stroke engines, in accordance with the preamble of claim 1.
Fuel injection devices of this kind are described in EP 0 629 265, by reference to FIGS. 13 to 19 thereof. They operate according to the so-called pump-injector (unit injector) system with impulse injection, wherein an initially accelerated partial stroke of an armature of a solenoid-operated injection pump is provided axially guided at one end, acting as a delivery plunger, in which a displacement of the delivered fuel occurs in the pump system without pressure being built up in the fuel fluid. During this initial partial stroke the delivery plunger or the armature absorbs kinetic energy and stores it, a predetermined flow space being available for the fuel displaced thereby, this flow space being assured by a fuel circuit in the pump system. Due to the fuel circuit being suddenly interrupted predeterminedly by a valve means arranged in the armature or delivery plunger and actuated by the armature movement during the zero-resistance advance stroke of the delivery plunger and due to the subsequent movement of the delivery plunger the latter releases its stored kinetic energy as a impulse in pressure to the partial amount of fuel present in a space portion of the circuit space formed by the circuit interruption or closed off separatelyxe2x80x94the so-called pressure spacexe2x80x94between the delivery plunger or therein and an injector closed e.g. spring-loaded. This abrupt pressure increase in the fuel to e.g. 60 bar results in the injector opening and fuel injected through the injector into a combustion chamber of an internal combustion engine during a extremely short time of e.g. a thousandth of a second.
These pump-injector systems known from EP 0 629 265 comprise a solenoid-operated reciprocating plunger pump 1 and the injector 2 (FIG. 1a). These pump-injector systems have a proven record of success particularly in two-stroke engines which formerly were notorious for heavy exhaust emissions due to so-called losses and high fuel consumption due to a high proportion of fuel being able to pass the discharge passage 3 unconsumed, because on two-stroke engines spill and discharge passage 3 are opened simultaneously. By means of the aforementioned pump-injector system the fuel consumption and exhaust emissions have now been drastically reduced. On top of this the poor smooth-running of the engine stemming from irregular ignition at low speeds has been almost completely eliminated. In this arrangement the fuel is injected extremely fast and directly into the combustion chamber 4 of a cylinder 5, i.e. not before the discharge passage 3 has been practically full closed. The control 6 for optimizing the pump-injector system is done electronically via e.g. a microprocessor which controls the injection timing and the amount of fuel injected, for this purpose the injection timing being established e.g. by means of a temperature sensor 7, a butterfly valve potentiometer 8 and a crank angle sensor 9. Expediently, the microprocessor also controls the ignition system 10 of the piston/cylinder unit of the engine charged with fuel by the pump-injector system.
Due to these pump-injector systems the hydrocarbon exhaust emissions as compared to those of other two-stroke engines are drastically reduced whilst simultaneously significantly improving smooth-running, especially at low speeds. Carbon monoxide and oil supplied for lubrication are also emitted in significantly reduced quantities so that such a two-stroke engine is comparable to a four-stroke engine as regards its exhaust emission performance whilst still exhibiting the high power-to-weight ratio typical of the two-stroke type.
In the aforementioned pump-injector systems the fuel circuit space is formed by a pressure chamber and a delivery plunger or armature space, the pressure chamber being the partial space portion separated from the pressure space by a standing pressure valve, the kinetic energy of the armature being transmitted to the fuel in this partial space portion and whereby the armature space is the partial space portion into which the fuel is able to flow displaced with zero resistance during the accelerated partial stroke.
In accordance with known pump-injector systems the armature space may be in connection with a fuel flood/scavenging means via a drilling in the housing so that fuel can be delivered through this partial space portion during the injection activity of the armature and/or during the starting phase of the pump or engine. Due to this flooding or scavenging action with e.g. cooled or bubble-free fuel the armature space is freed of fuel containing bubbles and it as well as its surroundings cooled whilst the formation of bubbles due to heat development and/or cavitation is practically eliminated.
In special instances, especially when the fuel is affected by heat, as may happen in the pump-injector system during operation, e.g. due to the electrical energy and/or armature friction or the like, bubbles may gain access to the pressure space. This may detriment functioning of the pump-injector system and, more particularly, injection.
In direct fuel injection as practised on Diesel engines it is known to configure injection so that initially a first amount of fuel is injected and on completion of ignition delay a second main amount of fuel is injected so that knocking of the Diesel engine is substantially reduced.
In this context two basic approaches are known, namely phased injection and dual injection. Dual injection can be achieved with two pump elements or with a very fast operating single pump element for injection twice. However, the complicated design necessary for this purpose has hitherto thwarted any practical application thereof, all the more so since it was assumed that thus would merely reduce engine knock but not reduce fuel consumption.
It is for this reason that phased injection became popular which is achieved by means of a pre-injection valve having two nozzle passages which open at differing pressures, as a result of which injection is divided into a prejet and a main jet.
It is known furthermore to implement by means of a dual injection a so-called charge stratification of the fuel in the combustion chamber of the engine.
In charge stratification of a spark ignition engine fuel is introduced into a combustion chamber of the engine such that a main amount of fuel forms a lean fuel/air mixture (e.g. l=1.5 to 3.0) and a rich fuel/air mixture (e.g. l=0.85 to 1.3) is enriched in the region of a spark plug. This rich fuel/air mixture is ignited by the spark plug, the lean fuel/air mixture non-ignitable as such then also being combustioned with a large excess of air. Due to this excess air highly favorable exhaust emission performance is achieved.
In the German engine trade journal MTZ Motortechnische Zeitschrift, year 35, Issue No. 10, October 1974, pages 307 to 313 two possibilities of generating charge stratification are cited. One approach to designing a charge stratification engine consists of directly injecting the fuel into a non-compartmented combustion chamber in which the stratification is produced by an oriented swirl of air, as a result of which the mixture in the vicinity of the spark plug is enriched, it remaining nevertheless ignitable even though as a whole it is very lean.
It is the pressure and direction with which the fuel is injected, the positioning of the spark plug relative to an injector and especially the air flow velocity which decisively influence proper functioning of this system. Since the intensity of the air swirl is proportional to the engine speed, difficulties arise in operating in the high speed/load regime as is typical and necessary in automotive engines.
Charge stratification may be achieved by a compartmented combustion chamber, i.e. with the aid of of an ancillary chamber. In this case a lean mixture is induced into one cylinder whilst enrichment takes place in the ancillary chamber by means of an injector or an additional intake system. Systems of this kind are basically independent of changes in speed and load and are thus well suited for automotive engines.
One such charge stratification engine having ancillary chambers is also described in the German engine trade journal MTZ Motortechnische Zeitschrift, year 34, Issue No. 4, April 1973, pages 130, 131. This charge stratification engine is Hondaxc2xds so-called CVCC engine incoporated in a compact car and achieving minimum CO, CH and NOx exhaust emissions. The drawback with this engine is that due to the ancillary chambers the efficiency is reduced and fuel consumption increased by approximately 10% as compared to conventional spark ignition engines having no ancillary chambers.
The invention is based on the object of providing a simple fuel injection device achieving reduced exhaust emissions, saving fuel and which is independent of mixture tolerances.
This object is achieved by a multiple injection device having the features of claim 1. The fuel injection device in accordance with the invention operates on the solid-state energy storage principle, as a result of which large amounts of fuel can be injected during short time intervals, and is configured double-acting, the fuel injection device in accordance with the invention exploiting a reciprocating or impulse and recoil movement of delivery plunger element during a working stroke both for initial injection by the impulse movement as well as for a subsequent injection by the recoil movement. Due to this arrangement the configuration of the fuel injection device is substantially simplified as compared to that of two separate injection devices, more particularly the number of parts required is reduced especially when the delivery plunger element is configured integrally.
With the fuel injection device in accordance with the invention precise and fast dual injection is achieved by simple ways and means so that in the combustion chamber an optimum fuel distribution and reliable ignition or combustion are achieved, as a result of which exhaust emissions are reduced and fuel saved. On top of this the engine can be operated with differing mixture qualities as regards the combustion air ratio (l) without ignition and combustion quality being detrimented by differing air quantities which are unavoidable in the cylinder in operation of the engine.
Advantageous aspects of the invention are characterized in the sub-claims.
Accordingly, the invention includes, more particularly, a pressure chamber in which the energy stored in the armature or in the delivery plunger element is transmitted to the fuel, in which the valve interrupting the zero-resistance displacement is configured outside of the armature space or arranged separate from the armature space and armature portion. Due to this arrangement the heat generated in the armature space is not directly transmitted to the pressure chamber, as a result of which heating of the fuel compressed during injection and thus the risk of bubbles forming is considerably reduced. On top of this the pressure chamber is freely accessible so that for further cooling it can be provided, for example, with cooling fins and/or directly with a fuel supply conduit to enable cool fuel free of bubbles to be supplied to the pressure chamber. Furthermore, the pressure chamber can be configured compact so that less fuel is present in the pressure chamber thus reducing the risk of bubbles forming.
In addition, due to the the pressure chamber being small and the fuel supply direct only minor amounts of fuel need to be scavenged.
Double or two-sided axial guidance of the armature in accordance with claim 5 avoids tilting movements of the armature causing friction so that heat development can be suppressed.
The formation of gas bubbles and their effect detrimental to proper functioning and/or heating up of the fuel are practically eliminated.
The fuel injection device in accordance with the invention can be put to use to particular advantage in the case of charge stratification. Since it works on the solid-state energy storage principle high ejaculation pressures can be generated over injection intervals which are extremely short in time, making fast repeat actuation possible at extremely high speeds (exceeding 10,000 rpm) for metering the fuel as a function of load with high accuracy.